Random Notes

IP prefix-list ip prefix-list provides the most powerful prefix based filtering mechanism Here is a quick little tutorial on Prefix-lists for you. A normal access-list CANNOT check the subnet mask of a network. It can only check bits to make sure they match, nothing more. A prefix-list has an advantage over an access-list in that it CAN check BOTH bits and subnet mask - both would have to match for the network to be either permitted or denied. For checking bits a prefix list ALWAYS goes from left to right and CANNOT skip any bits. A basic example would be this: 172.16.8.0/24 If there is only a / after the network (no le or ge) then the number after the / is BOTH bits checked and subnet mask. So in this case it will check the 24 bits from left to right (won't care about the last 8 bits) AND it will make sure that it has a 24 bit mask. BOTH the 24 bits checked and the 24 bit subnet mask must match for the network to be permitted or denied. No we can do a range of subn...

LSA types allowed per area type. Area Type 1&2 3 4 5 7 Backbone (area 0) Yes Yes Yes Yes No Non-backbone, non-stub Yes Yes Yes Yes No Stub Yes Yes No No No Totally stubby Yes No [*] No No No Not-so-stubby Yes Yes Yes No Yes

You need to remember how an access list wildcard mask works. 192.168.1.0 0.0.0.255 Where you have a 0 bit in the wildcard then the corresponding bit within the IP Address must match. So in the example above 192.168.1 must match. Where you have a 1 bit then the Wildcard mask does not care about the corresponding bit within IP address (also known as the 'don't care bit), thus the 255 in the last octect means that the corresponding bit within the IP address can be anything between 1 and 255. Therefore when matching routes with an access list, the access list would let through 'Prefixes' from: 192.168.1.0 to 192.168.1.255 Obviously within this range there would be no routes that are advertised as routes from a routing protocol (like broadcast), however it does capture everything. A Prefix list is far more precise 192.168.1.0/24 will only let through 192.168.1.0, if you wanted the prefix list to act like the access list, you would use the ge and le statements at th...